The present invention relates to a test fluid pipetting method, and more particularly, to such a method for pipetting and distributing each of a plurality of test fluids into a plurality of containers by means of a common pipetting apparatus.
By way of example, there have been proposed the multichannel type automatic analyzers which chemically and simultaneously analyze a plurality of components contained in a blood serum and other apparatus which automatically and simultaneously conduct multiple immunological inspections on the same test fluid based on agglutination by antigens and antibodies. In such apparatus, a plurality of test fluids are generally transferred successively (by picking them up) into respective containers and these test fluids in respective containers are pipetted and distributed successively into each of a plurality of reaction vessels corresponding to the number of analyzing items by means of a common pipetting apparatus. In the procedure in which successive test fluids are pipetted and distributed by means of the common pipetting apparatus, contamination and variation of concentration between test fluids being successively pipetted have an adverse effect upon results of the analysis. Therefore, it is necessary to effectively prevent such disadvantage.
By way of example, in an arrangement of an automatic chemical test apparatus disclosed in the Japanese Patent Publication No. Sho 50 - 17878, as shown in FIG. 1, a probe 1 for picking up and discharging a test fluid is connected through a tube 2 and couplings 3 and 4 to a pipetting syringe 5 and a syringe 6 for cleaning water and is connected through coupling 3 to a syringe 7 for forming an air layer. The pipetting operations of the arrangement are as follows. First, under the condition in which the probe 1 is immersed in water, the probe 1 and the tube 2 are cleaned by operating the syringe 6 and then water 8 is sucked into the probe 1 and the tube 2. Second, under the condition in which the probe 1 is placed in the air, air is drawn into the probe 1 by means of the syringe 7 and then upon once immersing the probe 1 into a test fluid held within a vessel a predetermined amount of the test fluid is sucked into the probe 1 by means of the syringe 5. Thereafter, the probe 1 is placed in the air and air is again drawn into the probe 1 by means of syringe 7. Subsequently, the probe 1 is immersed again into the same test fluid as previously sucked in and a predetermined amount of the test fluid is picked up by means of the syringe 5. Thus, as shown in FIG. 1, each layer of water 8, air 9, test fluid 10, air 11 and test fluid 12 is formed successively in the probe 1 and the tube 2. In this case, the test fluids 10 and 12 are the same but the test fluid 10 is for cleaning, not pipetted into a reaction tube. In addition, the test fluid 12 is drawn in in excess of the total amount to be pipetted into a plurality of reaction tubes.
After one of test fluids is drawn in as stated above, a part of the test fluid 12 is discharged into the test fluid vessel and then the test fluid 12 is successively pipetted by a predetermined amount thereof into a required number of reaction tubes. Subsequently, a surplus of the test fluid 12 and the test fluid 10 are discharged into a waste fluid vessel. Thus the pipetting and distributing operations of one of test fluids concerned are completed. Thereafter, the above sequential operations are repeated with regard to each of other test fluids to distribute the same into a plurality of the reaction tubes.
According to such pipetting and distributing method, the inner and outer walls of the probe 1 and the inner wall of the tube 2 are initially cleaned with water in the pipetting operations of each of test fluids so that it is possible to prevent occurrence of contamination between the successive test fluids being pipetted. Also, since the test fluid layer 12 to be pipetted into a plurality of reaction tubes is separated through air layer 11, test fluid layer 10 and air layer 9 from water layer 8, the dilution of the test fluid 12 by water 8 can be reduced and therefore it is possible to distribute the same test fluid having substantially a given concentration into each of reaction tubes. However, with the pipetting method, in which the same test fluid is picked up by separating it through air layers 9 and 11, it is necessary to pull out the probe 1 from the test fluid once while picking up it. Thus, the pipetting and distributing operations of each test fluid are time-consuming and hence it is impossible to conduct them rapidly.
Additionally, the Japanese Patent Laying-Open No. Sho 55 - 71950 discloses another pipetting and distributing method in which a test fluid in excess of the total amount needed for distribution is drawn into a fluid pipetting conduit into which a throwing-away liquid such as a diluent has been drawn, through an air layer and after the test fluid thus sucked in is partially discharged together with the throwing-away liquid which is ejected from another liquid conduit, the test fluid is pipetted in the similar manner as previously described into a plurality of reaction tubes together with a throwing-away liquid and subsequently the remaining test fluid and throwing-away liquid are successively discharged from the pipetting conduit to clean the inner wall of the latter. In such pipetting and distributing method in which a test fluid to be pipetted is drawn into the pipetting conduit by separating the test fluid from a throwing-away liquid through an air layer, there is no necessity for pulling out the pipetting conduit from the test fluid while drawing in the latter as in the pipetting and distributing method disclosed in the Japanese Patent Publication No. Sho 50 - 17878 described previously. Accordingly, it is possible to conduct the pipetting and distributing operations of a test fluid in a short time. However, when a test fluid to be pipetted and a throwing-away liquid for cleaning are separated through only an air layer, the test fluid within the pipetting conduit is subject to the influence of dilution by the throwing-away liquid adhered to the inner wall of the conduit during the previous cleaning in proportion as the test fluid within the conduit is substantially nearer to the throwing-away liquid. Consequently, when the test fluid drawn into the tube is pipetted and distributed to a plurality of reaction tubes by a given amount thereof, its concentration is reduced in proportion as the pipetting order is later, that is, the test fluid becomes closer to the throwing-away liquid, and general disadvantages are that it is hard to conduct an analysis with high accuracy.